Thundercat arcing, HT leads, Plug?

[drbaig]

Yesterday I noticed the ticking noise coming from the engine is indeed the plug arcing. I could see sparks from the plug cap to the cam cover.

Now this phenomenon is only occurring when the bike is hot up to temperature. Starts fine. Runs fine.

I checked the cap there is no damage.

Is it as simple as a worn out plug or a new HT lead?

I will post a video later after I get home from work.

https://www.youtube.com/watch?v=OwozRGUYUlI
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yzf 600r

[mudcow007]

can you remove the plug from the lead? some are molded on so you cant do anything with them

if it is removable, cut the lead down a touch an rescrew the plug back on

[stinkwheel]

I'd just replace the lot.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Fizzer Thou]

I thought that I was having a similar problem on my Exup.The silicone leads that I had fitted years ago all measured some misleading resistances with big differences between two short leads,so I replaced the leads with new copper core items and all new plug caps and it now runs far better

On closer inspection of the OEM plug caps I can see that where the caps are moulded together there is a crack that opens up when hot,causing the spark energy to dissipate to the cylinder head,which is the easier route than via the spark plug
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Just talk bikes.What else is there?

Always have a 'Plan B'

[drbaig]

[drbaig]

[drbaig]

A few months ago I took this video where I thought the clicking/ticking noise was header leak. At the end of the video there is a good angle at the plug cap and there are no sparks. I tightened the header and thought it was fixed since no noise.

https://www.youtube.com/watch?v=GU7niLVETgg

This following video is from this morning. I only noticed it yesterday after riding through heavy rush hour traffic filtering (new commute). The bike got quite hot and I could hear the ticking noise which I thought I had fixed by tightening header bolts.

https://www.youtube.com/watch?v=OwozRGUYUlI

I have also noticed that where the spark meets the plug cap there is discolouration there.

I think for a temporary fix I am going to insulation tape the cap and then revisit this problem when the weather is better.

I was also thinking if a simple fix of removing the cap and replacing that would be an option.
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yzf 600r

[Pjay]

That looks to me like there is some kind of wear/break on the Lead.
Electricity to arc, has to find a route to earth, so it must be coming through where the arcing is happening, or there must be something conductive on the lead or cover causing this. It might be solved with a new plug, which would cause a cleaner route to earth when sparking, but for sure, I would replace the lead as well, as this is certainly worn.

[Snod Blatter]

I had a pair of NGKs wear out at nearly 30K miles, to the point where the sparks were arcing down the outside to the head - this was apparently the path of least resistance! It also refused to fire on full throttle, as the spark in the combustion chamber was poor. New plugs sorted it right out.
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[Ariel Badger]

Run your hands over all of the components, after the first few shocks you will agree with Stinky's post and just replace the lot.
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Bikers make great organ donors, get 115 on your licence today.

[drbaig]

[Snod Blatter]

[RhynoCZ]

Does the engine even start when wet?
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[drbaig]

[weasley]

You can get the coils out with the carbs in place - getting the tank and airbox off isn't that big a job but the coils are a bit fiddly to get at. One more fiddle is getting at the central spark plugs, but with the right tool and some patience this is doable.

The plug caps simply unscrew from the HT leads, and the HT leads from the coils. The plug caps are supposed to have a 10kΩ resistance - one of mine went open circuit so I replaced it with a used one off eBay. For the leads, a quick fix, if you have the spare length, is to cut a little bit off the end and reattach the plug cap.

The plug caps are not cheap new, hence why I found some on eBay.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[RhynoCZ]

[drbaig]

[RhynoCZ]

As water shouldn't be even getting there, it's time for the new caps. Buy the proper ones, specified for your motorcycle. As you can see the spark plug caps have a rubber ring on them that seals the spark plugs in the head.

I've seen older bikes with no water damage around the plugs.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[drbaig]

Checked the plug 3.5 reading at 20k ohms.

Checked the cap 9.5 reading at 20k ohms.

So I am thinking it is the cables ?
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yzf 600r

[Snod Blatter]

Do the other plugs and caps read the same?
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[drbaig]

[drbaig]

Checked all the caps and plugs at 20k ohms

Cap 1 9.4
cap 2 12.3
cap 3 11.2
cap 4 9.6

Plug 1 3.75
plug 2 4.08
plug 3 3.73
plug 4 4.44

Put everything back and ran the bike for half an hour got it up to temp (100 degrees) no sparks, no ticking noise. Nothing. Maybe it was a lose cap ?

Or maybe it is an intermittent fault that will show up again at some point..
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yzf 600r

[ssray]

I usually when this happens, seal everything with either clear silicone(bathroom stuff) or silicone grease.
Remove leads and put a thin smear of either on the lead and the plug cap
Ray

[drbaig]

I think the culprit might be the spark plug.

I've changed the plug 1 and it's s not giving me any shocks when I touch the engine.

Although when I unplugged the cap 1 and started the engine with 3 other plugs capped I still got a shock from the cap 1. Is that normal? I mean the current has to go somewhere when is not going to the plug.
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yzf 600r

[ssray]